As a high molecular material having elasticity, generally employed are those obtained by mixing a natural rubber or a synthetic rubber such as diene polymer rubber or olefin polymer rubber (ex. ethylene-propylene-diene copolymer rubber) with a crosslinking agent, reinforcing agent, processing assistant and/or the like and crosslinking the resulting mixture under high temperature and high pressure conditions.
The above-described conventionally-used natural rubber or synthetic rubber however requires steps for crosslinking and molding or forming over a long period of time under high temperature and high pressure conditions so that it is poor in handling properties and productivity. In view of such drawbacks of the natural or synthetic rubber, various thermoplastic elastomers, similar to ordinarily used thermoplastic resins, from which a molded or formed product can be prepared easily by making use of the general-purpose melt molding or forming technique such as hot pressing, injection molding or extrusion have been developed recently.
As the prior art relating to a thermoplastic elastomer or its composition, known are:
(1) an elastomeric composition (Japanese Patent Application Laid-Open No. SHO 58-206644) which is obtained by mixing, with a view toward improving flexibility, thermal deformation resistance and mechanical strength, a block copolymer formed of an aromatic vinyl compound polymer block and a hydrogenated conjugated diene polymer block with a softener for a non-aromatic rubber and a propylene 1-olefin copolymer and optionally an inorganic filler; PA1 (2) an elastomeric composition (Japanese Patent Application Laid-Open No. SHO 59-131613) which is obtained by mixing, with a view toward improving flexibility, resistance to high-temperature compression set, mechanical strength, oil resistance and moldability or formability, a block copolymer formed of an aromatic vinyl compound polymer block and a hydrogenated conjugated diene polymer block with a softener for a non-aromatic rubber and a peroxide decomposition type olefin resin and optionally an inorganic filler; and PA1 (3) a hydrogenated block copolymer composition (Japanese Patent Application Laid-Open No. SHO 63-112649), which is obtained by mixing, with a view toward improving flexibility, high-temperature compression set resistance, high-temperature creep properties, mechanical strength, moldability or formability, oil resistance and anti-stickiness, a block copolymer formed of an aromatic vinyl compound polymer block and a hydrogenated conjugated diene polymer block with a softener for a non-aromatic rubber, a polyolefin resin, an olefin copolymer rubber and a reaction type alkylphenol/formaldehyde resin and then, subjecting the resulting mixture to dynamic vulcanization.
The above-described conventional elastomeric compositions (1) to (3) are recognized to have improved moldability or formability, oil resistance and compression set resistance to some extent, but do not have sufficient gas barrier properties, sealing properties and viscosity of the material itself. When these conventional elastomeric compositions are used for hermetically sealing materials such as packing material, sealant, gasket or stopper, they cannot be used effectively as hermetically sealing materials because of liquid leakage from the sealing stopper, liquid leakage after needle insertion and separation of broken pieces from the material by needle insertion.
In addition, a composition for medical material which is composed mainly of an isobutylene-polymer-block-containing block copolymer is known (Japanese Patent Application Laid-Open No. HEI 5-310868). Although the composition has a low adsorption amount level of a drug ingredient, it cannot be used effectively as a hermetically sealing material because of low compression set resistance and poor elastic recovery.
Among rubbers, a butyl rubber is known to have excellent gas barrier properties (Japanese Patent Application Laid-Open No. HEI 6-200098). When a mixture of a butyl rubber which serves as a main component with a block copolymer formed of an aromatic vinyl compound polymer block and an isobutylene polymer block is formed into a sheet, followed by curing under heat, the resulting product is a thermosetting type and has therefore insufficient moldability or formability. It is therefore difficult to obtain a polymer composition excellent in both moldability or formability and gas barrier properties.
Under such circumstances, there has been a demand for an elastomeric composition which has excellent flexibility, small high-temperature compression set, excellent elastic recovery, excellent properties such as mechanical properties, oil resistance and moldability or formability and besides, excellent gas barrier properties and excellent hermetically sealing properties; and can be used effectively as hermetically sealing materials. Materials which can satisfy such requirements are however not available at present.
An object of the present invention is therefore to provide a thermoplastic elastomeric polymer composition which has excellent moldability or formability and gas barrier properties, small compression set, excellent elastic recovery, good hermetically sealing properties and sealing properties and excellent flexibility, mechanical properties, oil resistance, safety and hygienic properties; and can be formed easily, similar to the ordinarily-employed thermoplastic polymer, by the general-purpose hot melt forming or molding method such as extrusion, injection molding or press molding.
Another object of the present invention is to provide hermetically sealing materials such as sealant, packing material and gasket and other molded or formed products by using the above-described thermoplastic polymer composition having excellent properties. In particular, a further object of the present invention is to provide hermetically sealing materials for a gasket for syringe or other medical tools and hermetically sealing materials used in the food-related field.